Magnetic field sensors have been commonly used in various electronic devices, such as computers, laptops, media players, smart phones, etc. There are several techniques/devices that can be used for detecting a magnetic field. Magnetoresistance (MR) magnetic sensor is a promising magnetic sensing technology for handset applications due to its advantages in sensitivity, power, and process cost compared with other magnetic sensors. MR magnetic sensors may include Giant Magnetoresistance (GMR) sensors, Anisotropic Magnetoresistance (AMR) sensors, Tunneling Magnetoresistance (TMR) sensors, or the like.
A TMR element is composed of two ferromagnetic layers separated by a non-magnetic, insulating tunnel barrier. One layer has a magnetization direction that is “free” to rotate in a magnetic field. The other layer has a “fixed,” reference magnetization that does not rotate when in a magnetic field of moderate to low strength that is of sensing interest. If the magnetization directions of the two layers are parallel to each other, the electrical resistance of the tunnel barrier is low. Conversely, when the magnetization directions are anti-parallel, the resistance is high. A magnetic field sensor based on TMR therefore converts magnetic field into electrical signal by a change in electrical resistance due to the changing angle of the magnetic free layer relative to the fixed layer in response to the field.
Magnetoresistance magnetic sensors, including TMR sensors, all suffer from cross-axis effects. While these sensors are designed to sense magnetic fields in one desired sensitive axis, there is a minor sensitivity to fields orthogonal to the sensitive axis. These orthogonal fields are called cross-fields or cross-axis magnetic fields. The cross-axis effect is characterized by the amount of on-axis sensitivity suppression due to cross-field intensity.
Cross-axis effects may occur from a number of sources, including fixed magnetic sources in the final use environment (i.e., a speaker magnet or inductor in cell phone) and dimensional characteristics of the MR element design. These cross-fields will create various amounts of cross-field error to the magnetic field in the desired sensitive axis.
Magnetic sensor output processing algorithms may compensate for offset and uniform sensitivity mismatch between axes, but not field dependent sensitivity differences. Therefore, reduction of cross-axis effects is crucial to sensor performance. It would be desirable to have a system, device, and method to effectively increase magnetic field measurement linearity and minimize cross-axis interferences.